Aspect ratio is the proportional relationship between width and height. Whether you're resizing images, setting video dimensions, or designing for screens, getting the ratio right prevents distortion.
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Open Aspect Ratio Calculator →What Is Aspect Ratio?
Aspect ratio is expressed as width:height. A 1920×1080 image has an aspect ratio of 16:9 (both numbers divided by their GCD of 120). Maintaining aspect ratio when resizing prevents images from appearing stretched or squished.
Common Aspect Ratios
| Ratio | Common Use | Example Resolution |
|---|---|---|
| 16:9 | HD video, most monitors | 1920×1080, 3840×2160 |
| 4:3 | Old TV, iPad | 1024×768, 2048×1536 |
| 1:1 | Instagram, avatars | 1080×1080 |
| 9:16 | TikTok, Instagram Stories | 1080×1920 |
| 21:9 | Ultrawide monitors | 2560×1080 |
| 3:2 | DSLR cameras, MacBook | 3456×2304 |
Calculate Missing Dimension
If you know a 1920×1080 image and want to resize to 1280 wide, maintaining 16:9:
New Height = 1280 × (1080 / 1920) = 720px
The calculator does this automatically — fill in 3 of the 4 fields.
CSS Aspect Ratio
/* Modern CSS — maintain 16:9 */
.video-container {
aspect-ratio: 16 / 9;
width: 100%;
}
/* Legacy padding trick */
.video-container {
position: relative;
padding-bottom: 56.25%; /* 9/16 = 0.5625 */
height: 0;
}Frequently Asked Questions
How do I calculate aspect ratio from dimensions?
Divide both dimensions by their Greatest Common Divisor (GCD). For 1920×1080: GCD is 120, so 1920/120 = 16, 1080/120 = 9 → 16:9.
What aspect ratio is my phone screen?
Most modern smartphones use 19.5:9 or 20:9 (taller than 16:9). Notch and rounded corners are excluded from the ratio.
Can aspect ratio be a decimal?
Yes — 2.39:1 (cinema) and 1.85:1 (widescreen) are common film ratios expressed as decimals.
Why does my cropped image look wrong?
Cropping changes both the content and the aspect ratio. Use the calculator to find the correct crop dimensions before applying.